The invention relates to a bus system with optical waveguides wherein the information signal to be transmitted is converted by an electro-optical transmitter into a light signal. This signal is coupled into an optical waveguide and transmitted thereover to an opto-electrical receiver where it is converted into an electrical use signal from which the information signal is regained. The system is particularly useful for multi-computer systems with a local optical bus with a star coupler.
Suitable transmission paths for the communication of computers with one another are required in local networks with multi-computer arrangements. The computers can be fundamentally interconnected as a star, as a ring, or over a bus. Extensive demands are made on the transmission circuit in a bus system, and specifically of the bus. For example, the transmission of the information must occur at a high rate and with high accuracy. Regaining the clock at the receive side requires a corresponding coding of the information. A collision recognition must be provided, this recognition occurring when a plurality of computers begin to transmit simultaneously.
It is known to construct multi-computer systems wherein an optical waveguide is employed for the bus (for example, Siemens Forshungs-und Entwicklungsberichte, Vol. 9, 1980, No. 1, pp. 33-37; IEEE Transactions on Communications, Vol. Com.-26, No. 7, July 1978, pp. 983-990, both incorporated herein by reference). In these multi-computer arrangements with an optical waveguide bus, the information signals are converted with the assistance of an electro-optical transmitter into light signals which are coupled into the optical waveguide by the transmitter. These signals are transmitted over the optical waveguide to the computers connected to the bus, and are transmitted with, for example, the assistance of a star coupler. An opto-electrical receiver can in turn convert the light signals back into electrical information signals which are then processed in the computer in the standard manner. AC-coupled, controlled-gain amplifiers have been hitherto employed for such opto-electrical receivers. The control time constants existing in such amplifiers, however, are an impediment in the bus operation since the level zero prevails on the bus between each transmitted information. Special codings, for example, the Manchester code, are employed at the receive side for regaining the clock, this resulting in a loss of band width. Alternatively, one may employ scramblers and PLL circuits which result in considerable expense. The collision recognition, finally, is carried out by means of information comparison. As a result, however, only the computers participating in the collision can perceive the collision.